What obvious? The command creates and returns a pidfd for the pid passed, not a process or a proc (which would be conflated with other concepts in Linux).
But you're opening the object (which already exists), not a file descriptor (which doesn't exist yet). And when you create or open a kernel object, you always get back a (new) file descriptor representing that object. See perf_event_open, mkfifo, etc. I'm not really sure how it'd have conflated with anything to call it proc_open or something like that, but I'll take your word on it.
